Outage Analysis-Human Nature or Chaotic Grids?

In Engerati’s The Future of Transmission and Distribution: Adapting networks to the challenges of renewable and sustainable electricity generation, the authors analyze the cause of outages and how grid operators can control them better.
Published: Tue 08 Jan 2013

If the main aim of energy providers is to run an uninterrupted supply precisely balancing energy input with output, then the antithesis of that aim is a power outage. The simplest reason for this is the imbalance in supply and demand when attempts are made to utilize more power than what has been generated. In practice, an imbalance is less likely to be at the base of any particular outage than a failure, in some way, of transmission, where there is enough energy in the grid to supply overall needs. However, due to congestion or line breaks, that energy cannot be transmitted fast enough to meet those needs.

Outages are often caused by a number of combined factors such as an act of god and system or regulatory failures. The immediate physical trigger for an outage could be due to adverse weather conditions or even an overhanging branch. Although operators can’t control these events, they should plan for them by putting processes and systems in place. This is particularly relevant to an electricity grid where energy will follow the path of least resistance and where uncontrolled energy flows can have unpredictable financial and physical consequences.

A common cause of a major blackout is the cascading outage. This is when failure in one part of the system places greater strain on other parts which are often better guarded. Those parts of the grid then go down, taking out even more critical connections and components. As a result, a small initial failure can quickly lead to a major outage.

The known techniques for containing cascading outages include the ability to:

  • Run grids at higher capacity margins
  • Isolate critical fault areas
  • Re-route power flows

Outage and regulatory framework

Ultimately, whether a grid operator has the ability to apply the above techniques and whether a grid is managed by individuals who are sufficiently experienced to apply them, depends on decisions taken about investment, training, planning and processes. This responsibility lies firmly on the shoulders of grid operators.

There must be a proportionate balance between penalties levied on grid operators for failure to put in place investment that support architecture and the chilling effect of a “too much blame” culture. If penalties are too high, operators are likely to take refuge in process, substituting defensive tactics for proactive grid management.

Many believe that there are a number of jurisdictions across the world, including the US and India, where the regulatory regime and associated penalties for grid failure are too mild. While grid operators are largely to blame for outages, there are other grid management aspects which they cannot control. One example is the escalating introduction of intermittent renewable sources, backed by government subsidy, which places more pressure on the national power grid.

Outage and renewables

Renewable energy risks creating outages in two ways:

  • Power surges-creating more capacity than can be safely dispersed within the time available
  • Sudden power drops-creating sudden demand at locations geographically distant from the original generation locus, and stressing the transmission grid between those two locations.

Pushing energy providers to increase their reliance on renewables can increase the likelihood of stressing their own and neighboring grids. This adds cost that may offset some of the financial benefit of investing in renewables.

Widening the grid

The idea of extending the grid is attractive as it will offer larger reserves. This makes it easier to balance supply and demand as peaks and troughs should even out. A larger grid will also enable some renewables, particularly wind, to be closer to baseload. Statistically, wind energy generated at a single point can vary from zero to some theoretical maximum. Wind energy generated at two distantly located points is less likely to be zero and, as more widely separated locations are added to a grid, so the amount of energy generated will tend to fluctuate within much narrower limits around a grid average for that source. Widening the grid will more likely lead to smaller outages and to more infrequent but larger outages.

Widening of the transmission and distribution (T&D) grid is constrained both physically and financially. Investments in erecting additional higher capacity HVDC lines can resolve physical limits. In some areas, (for example, between the East and West of Japan) more complex arrangements are needed as the issue is not capacity but one that is related to the operating characteristics of the two separate grids.

The widening of the grid across boundaries is problematic in the short term. This is taking place between states (Europe and Asia) and between independent system operators and regional transmission organizations (in the US, for example).  One concern is that energy, which is subsidized in one state, could end up being used elsewhere. Energy may be supplied across grid boundaries from one pricing and regulatory regime to another. This could create anomalies in a free market environment as energy providers exploit loopholes to gain excess profit.

Another concern is how to deal with investments made in one national energy grid on the basis that by being a net exporter of energy it is able to obtain a lower marginal cost of generation for its own population: what then happens if that supplier is undercut by a supplier in a third country, leaving it with excess capacity that, by virtue of being under-used, is actually more expensive than it would have been.

The real issue is to do with the allocation of marginal benefits around a competitive network which is in the process of evolving, not as a unified whole, but as a series of independent components. As with other grid development aspects, uncertainty as to how the overall system will evolve over the next two decades creates a substantial risk for potential investors. This can be viewed as a significant disincentive for investment.

The inevitability of outages in transmission and distribution

The combination of physical, systemic and regulatory failings which cause grid failure is logical is viewed as the totality of issues to be resolved in “fixing” grids. A hint that an alternative viewpoint needs to be found, lay in the way that cascading outages manifest, bearing a strong resemblance to the “butterfly effect” of chaos whereby a small variation in initial parameters may significantly alter how a given situation plays out. For instance, falling leaves may take out a single transmission line, the fault may quickly balance out, and no significant damage follows. However, it is also possible for the leaf to take out a small local line, causing congestion in several other lines, overloading one substation, adding further congestion elsewhere in the network, and rapidly bringing down power across an entire region. Therefore, failures are inevitable and unpredictable.

Some analysts say that increased complexity and an inverse power law dictate that the longer a system survives without a major outage, the worse the scale of that outage when it arrives. While such a view remains almost heretical as far as many in the industry are concerned, it gives rise to significantly different recommendations as to how the industry should approach outages.

Engerati Analysis

Outages are inevitable and it is not productive for grid operators to devote all their resources to minimize outages. Major outages can be reduced in frequency but they will not be completely eliminated. Therefore, grid operators should educate the public how to handle major outages. It should be accepted that higher capacity is costly and may lead to an increase in minor outages. A different approach to grid management is needed such as flow control devices. Elements of the smart grid will help to improve grid management.

Sources                                            

Engerati-The Future of Transmission and Distribution: Adapting networks to the challenges of renewable and sustainable electricity generation